19.1 Earthquakes

elastic deformation

causes material to bend and stretch

fault

fracture or system of fractures in earths crust that occurs when stress is applied too quickly, or stress is too great

plastic deformation

permanent deformation caused by strain when stress exceeds a certain value

epicenter

point on earths

strain

the deformation of materials in response to stress

focus

the point of initial fault rupture where an earthquake originates that usually lies at least several kilometers beneath earths surface

secondary wave

the seismic wave that causes rock particles to move at right angles to the direction of the waves

primary wave

the seismic wave that squeezes and pushes rocks in the came direction that the wave travels

stress

the total force is acting on crustal rocks per unit of area.

seismic wave

the vibrations of the ground during an earthquake